In certain instances, the manufacturer wants you to use their product images and will make them available via download on their website (Pipedreams is an example of a company that does this). As long as you don't hot-link (steal their bandwidth), this is fine.
Pictures taken by third-parties — for example, something Google images pulls up from a blog site during a search — should never be used in reviews unless you have the owner's permission.
Pictures from Wikipedia, licensed under the very generous Creative Commons 3.0, should also not be used since EF is a business site, and there is remuneration for the reviews.
Roland wrote an interesting article for SEXIS which relates to this topic: